Trait Application 

pub trait Application: Send + Sync {
    // Provided methods
    fn create_payload(&self, _ctx: &BlockContext<'_>) -> Vec<u8>  { ... }
    fn validate_block(&self, _block: &Block, _ctx: &BlockContext<'_>) -> bool { ... }
    fn validate_tx(
        &self,
        _tx: &[u8],
        _ctx: Option<&TxContext>,
    ) -> TxValidationResult { ... }
    fn execute_block(
        &self,
        _txs: &[&[u8]],
        _ctx: &BlockContext<'_>,
    ) -> Result<EndBlockResponse> { ... }
    fn on_commit(&self, _block: &Block, _ctx: &BlockContext<'_>) -> Result<()> { ... }
    fn on_evidence(&self, _proof: &EquivocationProof) -> Result<()> { ... }
    fn extend_vote(
        &self,
        _block: &Block,
        _ctx: &BlockContext<'_>,
    ) -> Option<Vec<u8>> { ... }
    fn verify_vote_extension(
        &self,
        _extension: &[u8],
        _block_hash: &BlockHash,
        _validator: ValidatorId,
    ) -> bool { ... }
    fn query(&self, _path: &str, _data: &[u8]) -> Result<Vec<u8>> { ... }
    fn list_snapshots(&self) -> Vec<SnapshotInfo> { ... }
    fn load_snapshot_chunk(&self, _height: Height, _chunk_index: u32) -> Vec<u8>  { ... }
    fn offer_snapshot(&self, _snapshot: &SnapshotInfo) -> SnapshotOfferResult { ... }
    fn apply_snapshot_chunk(
        &self,
        _chunk: Vec<u8>,
        _chunk_index: u32,
    ) -> ChunkApplyResult { ... }
    fn tracks_app_hash(&self) -> bool { ... }
}

Application interface for the consensus engine.

The lifecycle for each committed block:

1. execute_block — receives all decoded transactions at once; returns validator updates and events
2. on_commit — notification after the block is finalized

For block proposal:

• create_payload — build the payload bytes for a new block

For validation (before voting):

• validate_block — full block validation
• validate_tx — individual transaction validation for mempool

For evidence:

• on_evidence — called when equivocation is detected

All methods have default no-op implementations.

Provided Methods

fn create_payload(&self, _ctx: &BlockContext<'_>) -> Vec<u8>

Create a payload for a new block proposal. Typically pulls transactions from the mempool.

If your mempool is async, use tokio::runtime::Handle::current().block_on(..) to bridge into this synchronous callback.

fn validate_block(&self, _block: &Block, _ctx: &BlockContext<'_>) -> bool

Validate a proposed block before voting.

fn validate_tx( &self, _tx: &[u8], _ctx: Option<&TxContext>, ) -> TxValidationResult

Validate a single transaction for mempool admission.

Returns a TxValidationResult with valid and priority. Priority determines ordering in the mempool (higher = included first).

An optional TxContext provides the current chain height and epoch, which can be useful for state-dependent validation (nonce checks, etc.).

fn execute_block( &self, _txs: &[&[u8]], _ctx: &BlockContext<'_>, ) -> Result<EndBlockResponse>

Execute an entire block in one call.

Receives all decoded transactions from the block payload at once, allowing batch-optimised processing (bulk DB writes, parallel signature verification, etc.).

Return EndBlockResponse with validator_updates to schedule an epoch transition, and/or events to emit application-defined events.

fn on_commit(&self, _block: &Block, _ctx: &BlockContext<'_>) -> Result<()>

Called when a block is committed to the chain (notification).

fn on_evidence(&self, _proof: &EquivocationProof) -> Result<()>

Called when equivocation (double-voting) is detected. The application can use this to implement slashing.

fn extend_vote( &self, _block: &Block, _ctx: &BlockContext<'_>, ) -> Option<Vec<u8>>

Generate a vote extension for the given block (ABCI++ Vote Extensions). Called before casting a Vote2 (second-phase vote). Returns None to skip extension (default behavior).

fn verify_vote_extension( &self, _extension: &[u8], _block_hash: &BlockHash, _validator: ValidatorId, ) -> bool

Verify a vote extension received from another validator. Called when processing Vote2 messages that carry extensions. Returns true if the extension is valid (default: accept all).

fn query(&self, _path: &str, _data: &[u8]) -> Result<Vec<u8>>

Query application state (returns opaque bytes).

fn list_snapshots(&self) -> Vec<SnapshotInfo>

List available state snapshots for state sync.

fn load_snapshot_chunk(&self, _height: Height, _chunk_index: u32) -> Vec<u8>

Load a chunk of a snapshot at the given height.

fn offer_snapshot(&self, _snapshot: &SnapshotInfo) -> SnapshotOfferResult

Offer a snapshot to the application for state sync.

fn apply_snapshot_chunk( &self, _chunk: Vec<u8>, _chunk_index: u32, ) -> ChunkApplyResult

Apply a snapshot chunk received during state sync.

fn tracks_app_hash(&self) -> bool

Whether this application produces and verifies app_hash state roots.

Applications that do not maintain a deterministic state root (e.g. the embedded NoopApplication used by fullnodes without an ABCI backend) should return false. Sync will then bypass the app_hash equality check and accept the chain’s authoritative value, allowing the node to follow a chain produced by peers running a real application.

Implementors

impl Application for NoopApplication